1. Field of the Invention
The present invention relates to a camera diaphragm control device which measures light from an object of interest through an objective lens and a diaphragm aperture in process of being stopped down, thereby arresting the diaphragm to determine a diaphragm aperture when the output of the light measurement represents a given relationship with a reference signal, and more particularly it pertains to such a type of camera diaphragm control device which simplifies flash photography using an automatic flash light control in an electronic flash device (hereinafter called merely "strobo").
2. Description of the Prior Art
For flash photography using a strobo, it is convenient if a diaphragm aperture is automatically set to a specific aperture for flash photography such as F5.6, which can most probably provide a satisfactory photograph for the characteristics of an objective lens.
However, conventional diaphragm control devices of such a type arrest a diaphragm at a maximum aperture (fully open aperture) in a low brightness condition necessitating a flash illumination and therefore cannot automatically set the diaphragm to such a specific aperture for flash photography.
In co-pending patent application Ser. No. 56,938 filed on July 12, 1979 and assigned to the same Assignee, there has been proposed a camera flash photography system which enables a diaphragm to be stopped down even in a low brightness condition by the aid of a preliminary flash light produced by a strobo prior to the production of a primary flash light, with its intensity maintained substantially constant for a duration covering the period of time until automatic setting of the diaphragm is completed. With this system, the diaphragm is arrested when the output of the light measurement effected through the diaphragm aperture being reduced indicates a given relationship relative to a reference potential during the production of the preliminary flash light. This system, although entirely satisfactory for its intended purpose, incurs one drawback in that the automatically set diaphragm aperture varies depending on the object distance such that a long object distance may cause the diaphragm to be automatically set at the maximum aperture because the reference potential is fixed by a guide number setting of the strobo. The automatic setting of the diaphragm to the maximum aperture due to a long object distance reduces the depth of the field and frequently results in unsatisfactory photography. Further, as most objective lenses have aberrations poorly corrected for the maximum aperture, the automatic setting of the diaphragm to the maximum aperture may degrade the photographic image and this may also result in unsatisfactory photography.